Electric contact



Patented Nov. 12, 1940 2.221.286 Emc'rmc CONTACT Franz R. Hensel,Kenneth L. Emmert, and James W. Wiggs, Indianapolis, Ind., assignors toP. R.

Mallory & 00., Inc., poration of Delaware No Drawing. App

Indianapolis, Ind., a

lication April 9, 1940,

SerialNo. 328,688

I Claims.

This invention relates to electrical contacts.

The present application 'is a continuation in part of prior-filedco-pending application Serial No. 258,183, filed February 24, 1939.

A general object of this invention is the provision of electricalmake-and-break contact hav ing improved operating characteristics.

A more specific object of the invention is the provision of electricalmake-and-break contacts which have, due to the composition thereof, a

reduced contact resistance, less tendency for arcing, pitting andtransferring during the operation and which overcome particularly thedanger of sticking or fusing together.

Other objects of the invention will be apparent from the followingdescription taken in connection with the appended claims.

The present invention comprises the combination of elements, methods ofmanufacture and the product thereof brought out and exemplified in thedisclosure hereinafter set forth, the scope of the invention beingindicatedin the appended claims.

The present invention contemplates the use of boron in proportionsranging from 0.01% to 10%,

balance substantially all silver. It is also contemplated that theaddition of boron can be utilized to effect improvements in silver basecontact materials which may contain, in addition to silver, auxiliarymetals from the iron group such as iron, nickel and cobalt andingredients which wholly or partially alloy with silver such as copper,gold, platinum, palladium, silicon, cadmium,

zinc, magnesium, tin, manganese or other con- 5 tact metals.

The preferred ranges of percentages of the ingredients are as follows:

-55. Silver 'has advantageous characteristics for contacts when usedalone orlin its alloys. The

addition of boron adds further desirable characteristics to the contactsand, in several respects, supplements the advantages of silver. Ourpreferred method of making contacts of silver and boron consists ofmixing the powders of silver and boron, pressing, and then sinteringthem at a temperature below the melting point of silver, preferably in aneutral or reducing atmosphere. Another method we have found suitable isto press these materials cold and then apply a repressing operation atan elevated temperature such as 300 to 500 C. and then. sinter thematerials after such an operation. After sintering, the materials canagain be repressed or be converted by hammering, rolling or swaging orother operations into any suitable form or shape from which contacts canbe fabricated either by punching, heading, cutting or similaroperations.

Where the auxiliary ingredients are used with the silver they may firstbe combined with the silver to form a silver base alloy or composition,which is then reduced to powder and mixed with the boron powder or theymay be added as apowder to the mixture of silver and boron.

Boron of fine particle size is preferred. The. boron prevents thesticking together of co-operating contacts when they are subjected tocurrents tending to cause fusion. at the contact surface. It is thoughtthat the boron particles form a conductive layer between the silver ofthe two contacts and thus prevent direct fusion together of the metal ofthe two contacts. Boron is excellently suited for this purpose due toits high melting point whichis in the neighborhood of 2500" 0. Moreover,,boron forms oxides which have great dissolving power for other-metallicoxidesand therefore keep the contacting surfaces clean. 1

Another advantage of the new combination is that it will lend itselfmore readily to silver brazing of the contacts to backings than willmaterials of the prior art such as silver-graphite andsilver-molybdenum. Materials of the prior art such as silver-graphiteare very difficult to braze because the silver solder does not wet thegraphite and therefore the adhesion and the strength of such silversolder joints are very poor. In the case of silver boron the conditionsare quite difl'erent because the boron forms some boric acid or itsanhydride, which acts as a flux for the silver solder, cleaning thesurfaces to be brazed together.

In some cases it is proposed to back up the boron-silver contact layerby a solid metal layer and produce a bi-metallic structure consisting onone side of boron silver and the other side 01 a metal or alloy such assilver not containing any boron, iron, copper, nickel or other metal.Such bi-metallic strips can be cut into suitable sizes and attached tothe backing by any suitable means. 7

While the present invention as to its objects,

has been described herein as carried out in speciflc embodiments thereofit is not desired to be limited thereby but it is intended to cover theinvention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An electric contact formed of a metal composition of boron from 0.01to 10% and the balance predominantly silver, said boron being in theform of finely divided particles interspersed with and bonded by saidsilver.

2. Am electric contact formed of a metal composition of 0.1 to 10%boron, balance silver, said boron being finely divided and interspersedwith and bonded by said silver.

3. An electric contact formed of a metal composition of finely dividedboron from 0.01 to and silver as the bonding agent therefor, metalselected from the group consisting of iron, cobalt and nickel comprising5 to 50% of said composition contained in said silver, said silverforming substantially all of the balance of said com-position.

4. An electric contact formed 01' a metal com position of 0.01 to 5%boron, 5 to 50% of metal selected from the group consisting of ironcobalt and nickel and the balance silver.

5. An electric contact formed of a bonded metal composition of boronfrom 0.01 to 5% and the balance a silver base alloy containing 0.5 to30% of alloying ingredients selected from the group consisting ofcopper, gold, platinum, palladium, cadmium, zinc, manganese, magnesiumand tin, said boron being finely divided and interspersed and bondedwith said silver base alloy.

FRANZ R. HENSEL.

